Development of Pt and Pt-Fe Catalysts Supported on Multiwalled Carbon Nanotubes for Oxygen Reduction in Direct Methanol Fuel Cells.

Pt and Pt-Fe catalysts supported on multiwalled carbon nanotubes (MWCNTs) were prepared by impregnation and reduction at intermediate temperature (400°C). The MWCNTs with diameters ranging from 20 to 100 nm were synthesized by a spray pyrolysis technique. Pt/MWCNTs and Pt-Fe/MWCNT catalysts were characterized by X-ray diffraction, X-ray fluorescence, scanning electron microscope-energy dispersive X-ray analysis, and transmission electron microscopy techniques. The electro-catalytic behavior for the oxygen reduction reaction was investigated in rotating disk electrode configuration in an acidic medium, also in the presence of various methanol concentrations (0.01, 0.1, and 1 M). An anodic shift of the peak potential for methanol oxidation of ~150 mV was observed in the presence of 1 M methanol concentration for the Pt-Fe catalyst compared to the Pt catalyst. Both materials were used as cathodes in a direct methanol fuel cell at 30 and 60°C. A better performance was obtained for the cell based on Pt-Fe/MCWNTs as cathode catalyst. Although slight iron dissolution was observed after two weeks of discontinuous operation, the performance of the Pt-Fe catalyst was larger than the Pt catalyst. [ABSTRACT FROM AUTHOR]